how to change DXT1 to DXT5

i already finish my edited shoes.. but how can i change it from dxt1 to dxt5??? and i dont know how to use the DXTBmp.. plzzzz i need help.. can someone give me a tutorial lesson??? thanks a lot...

if you have the DXTBmp you need to take the picture to it and you have option to change it by save it as dxt5 or dxt1

there has a DXT5 in previews but i dont know how to save it..

you might find it easier to deal with GIMP
viewtopic.php?f=144&t=82787#p1436371

tnx man